One such device is known from German Patent DE 43 37 718 C1, which is used to detect marks that have contrast patterns, and in particular to detect bar codes.
The transmitted light beams emitted by a transmitter are guided across the marks. The received light beams reflected from the marks have an amplitude modulation corresponding to the contrast pattern of the applicable mark.
The reception signals present at the output of the receiver because of the received light beams are evaluated in an evaluation unit, which has an n-bit analog/digital converter and an arrangement of digital filters. The analog/digital converter, which preferably has a word width of 8 bits, converts the analog reception signal into a digitized reception signal. This digitized reception signal is delivered to the arrangement of digital filters. The coefficients of the digital filters are selected such that the digital filtration compensates for signal distortions in the reception signal that are caused by component tolerances of the components used in the optoelectronic device.
The detection sensitivity of the optoelectronic device can be enhanced as a result.
From German Patent Disclosure DE 198 42 352, a further optoelectronic device for detecting marks, especially bar codes, is known. In this device, a transmitter is used that emits transmitted light beams in the blue wavelength range.
In comparison to optoelectronic devices that use transmitters that emit transmitted light beams in the red or infrared wavelength range, in this device, with increasing distance, a slower widening of the beam diameter of the transmitted light beams takes place. As a consequence, the transmitted light beams, even at relatively great distances from the device, still have such a small beam diameter that secure detection of the marks is assured.
Thus by the use of such transmitters, a great depth of field, within which marks are detectable, is obtained.